Issue #6598: Avoid clock wrapping around in test_make_msgid_collisions.

Use time.time instead of time.clock.

Lib/email/test/test_email.py

@@ -2424,7 +2424,7 @@ Foo
                 self.msgids = []
                 append = self.msgids.append
                 make_msgid = Utils.make_msgid
-                clock = time.clock
+                clock = time.time
                 tfin = clock() + 3.0
                 while clock() < tfin:
                     append(make_msgid())